There are known honeycomb structural bodies, in which catalyst is supported, capable of purifying exhaust gas emitted from an internal combustion engine of motor vehicles, etc. For example the honeycomb structural body is comprised of partition walls arranged in a lattice shape and a plurality of cells formed by the partition walls. The honeycomb structural body is mounted to an exhaust gas passage through which exhaust gas is passing. When exhaust gas having a high temperature flows through the honeycomb structural body mounted to the exhaust gas passage, catalyst supported in the honeycomb structural body is activated by the exhaust gas of a high temperature, and purifies the exhaust gas.
Recently, because vehicles emission control for reducing motor vehicle emissions becomes stricter year by year, there is a strong demand of further decreasing harmful materials (cold emissions) generated immediately when an internal combustion engine starts. In order to solve this problem, it is requested to arrange the honeycomb structural body as close as possible to the engine and quickly increase a temperature of the honeycomb structural body to activate catalyst. Thus, it is requested for the honeycomb structural body to have a high exhaust gas purification performance and a high thermal shock resistance.
For example, a patent document 1 has disclosed a honeycomb structural body and defines a relationship in a catalyst amount, a surface area, a cell density, etc. between a central section and an outer peripheral section. Further, a patent document 2 has disclosed a honeycomb structural body and defines a relationship in an opening ratio, an absorbing rate, etc. between a central section and an outer peripheral section. In addition, a patent document 3 has disclosed a honeycomb structural body having an inner skin section formed between a first cell section (i.e. a central section) and a second cell section (i.e. an outer peripheral section), and defines a relationship in a cell density, etc. between the first cell section and the second cell section.
Further, a patent document 4 has disclosed a honeycomb structural body in which the number of web frames (i.e. partition walls) formed in a radial direction from a central side to an outer peripheral side is changed. Still further, a patent document 5 has disclosed a honeycomb structural body in which partition walls have a shape protruded from a central point toward an outside, and a cell density of a central section is smaller than a cell density of an outer peripheral section. Still further, a patent document 6 has disclosed a honeycomb structural body comprised of a plurality of honeycomb segments assembled together to form a monolithic body. The patent document 6 has shown a relationship in a thickness of a partition wall, a cell density, etc. between the outermost honeycomb segment, which forms an outermost peripheral surface, and the other honeycomb segments which do not form the outermost peripheral surface.